Nuclear Chemistry

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AP Chemistry Chapter 23 Notes
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• Henri Becquerel ruined some photographic
  plates with x-rays from a uranium source and
  radioactive decay was discovered in 1896.

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Henri Becquerels experiment (1896) Tried to
see if fluorescent minerals would give off
X-rays. Set some out in the sun with covered
photographic film. If minerals gave of X-rays
when they fluoresced, the film should darken
and it did. Accidentally set some of these
minerals in a dark drawer for a few days with
undeveloped film, and was surprised to see the
film strongly exposed. He knew they gave off
X-rays when charged by the sun - but these
results suggested the X-rays were coming from the
mineral itself Natural Radioactivity No
external energy source required!
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Radioactivity

• One of the pieces of evidence for the fact that
  atoms are made of smaller particles came from the
  work of Marie Curie (1876-1934).
• She discovered radioactivity, the spontaneous
  disintegration of some elements into smaller
  pieces.

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Marie and Pierre Curies experiments with
pitchblende Discovered Radioactive Naturally
occurring elements, particularly Uranium, Radium,
and Polonium. Curium was named after Marie
posthumously
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THE GREAT DISCOVERY W.K. Roentgens experiment
(1895) - Fluorescence Certain substances will
absorb photons of energy when exposed to a source
(i.e. cathode rays, the sun), and then emit them
over a period of time thus they glow in dark
when exposed to UV light Cathode rays beams of
electronsCathode ray tube (CRT) Vacuum tube
that has electric current passed through it
. Component of television sets thats why they
call it the tube 
X-rays Name given by Roentgen to unusual stray
energy observed to cause fluorescence across the
room when CRT was used X-ray because he did not
know what the heck it was.and the name stuck
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BETA PARTICLES

• Consists of high speed electron (from
  disintegration of neutron)
• Tissue damage potential much greater than Alpha
• Harmful if ingested? not as much as Alpha
• Can be blocked? by glass, will penetrate skin

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GOLD FOIL EXPERIMENTErnest Rutherford and the
Gold Foil Experiment   Disproved Thompsons
plum pudding model Proved the existence of a
nucleus with a positive charge 
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ALPHA PARTICLES

• Consists of He nucleus
• Tissue damage potential great if internalized
• Harmful if ingested? yup, very
• Can be blocked? by layer of skin, or cardboard

• Note that atoms are NOT conserved in nuclear
  reactions, but mass numbers and atomic numbers
  are.

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NUCLEAR RADIATION Ernest Rutherford and the
Lead block experiment (1899) - Alpha rays
(?)Beta rays (?)Gamma rays (?)
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How did Rutherfords gold foil experiment change
the theory of the structure of the atom?
Thompson 1906
Rutherford 1913
Bohr 1924

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• ARCHITECTURE OF THE ATOM
• Atomic Number Number of protons
• Determine what type of element an atom is
• Mass Number Sum of total number of protons and
  neutrons in an atom
• Can change for an element depending upon the
  number of neutrons present
• Isotopes Elements with the same atomic number,
  but different mass numbers
• Due to the difference in number of neutrons
• Example
• C-14 and C-12
• H-1, H-2, and H-3
• Radioisotope Isotope that is unstable and
  undergoes decay, thus giving off radiation
•    

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Subatomic Particles
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Common Isotopes
Isotopes of Particular interest C-14 used in
radiocarbon dating I-131 used in thyroid cancer
treatment U-235 used in nuclear power
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ISOTOPES IN NATURE Atomic Mass -Weighted Average
mass of all existing isotopes of an element  Can
be calculated by (percent isotope 1)(molar mass
isotopes 1) (percent isotopes 2)(molar mass
isotope 2) ..  Try this with your grades as
an example. Final grades will be determined by
giving homework 10, labs 30, and tests
60Homework grade 85 Lab grade 80 Test
grade 60  Final grade (.10)(.85)
(.30)(.80) (.60)(.60) .69  
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Nuclear Section B Introduction
Approx. 90 known naturally occurring elements
Approx. 350 known isotopes in our solar system
Approx. 70 of these radioactive
Radioactive just means unstable it naturally
decays
Approx. 1,600 Lab created isotopes
There is a rather constant level of natural
radiation in our environment called background
radiation
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TABLE OF CHANGES RESULTING FROM NUCLEAR DECAY
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Spontaneous Radioactive Stability

1. Production of an ? particle
2. Production of a ? particle
3. Production of ? rays
4. Spontaneous Fission

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1. production of a particle
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2. production of b particle
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3. production of g rays
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4. Spontaneous Fission
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DECAY SERIES Shows the nuclear decay steps that
occur when a radioactive isotope decays to a
final stable product
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II. Nuclear Fission
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• Sub-Critical
• Critical
• Supercritical

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then radioactive decomposition
½ life 1.3 sec
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then radioactive decomposition
½ life 1.3 sec
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then radioactive decomposition
½ life 18.3 months
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then radioactive decomposition
½ life 18.3 months
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Other Types of Nuclear Reactions
K-capture the capture of an electron from the
first or K shell
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Other Types of Nuclear Reactions

• Positron (01b) a positive electron

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Formation of a Neutron
An electron and proton combine to form a
neutron. 0-1e 11p --gt 10n
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• Less
• mass

more protons
fewer protons
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III. Nuclear Fusion Example 1

• Requires 40,000,000 K to
• overcome electrostatic repulsion

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• Half life
• SM x (1/2)n EM
• (1/2)n EM / SM or EM / SM (1/2)n
• n log (1/2) log (EM / SM)
• n log (EM / SM) / log (1/2)
• n t / t1/2 life

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• ln (N/No) ln (1/2)n
• ln (N/No) - kt
• t1/2life k ln (1/2) 0.693
• t1/2life 0.693/k
• A kN

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thus, N/No?t - kN1 where N amount conc
or counts and k rate constant ? dN/dt
- kN
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Half-life time when
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Half-life
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Binding Energy energy released during
degradation of a nucleus
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E mc2
Energy mass x speed of light2
1 gram of mass 9 x 1013 joules amount of
energy needed to power your house for 1,000 years
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E mc2 or ?E c2?m where c 3.00 x
108 m/sec
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SOURCES OF EXPOSURE TO IONIZING RADIATION
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Nuclear Fission Splitting of an atom into 2 or
more daughter particles If daughter particles
are unstable, then they will be radioactive
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Particle Accelerators
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Fission Chain Reaction
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• Hydrogen bombs

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Results of fission reactions
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IONIZING RADIATION HOW MUCH IS SAFE?

• Rem Roentgen equivalent to man
• 1Rem 1000 mRem
• Does not matter what type of radiation it is, it
  still has the same ionizing effect on living
  tissue
• 1 mRem of exposure to radiation increases risk of
  cancer death by 1 in 4 million
• Two things to consider
• Radiation density
• Radiation dose

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RADIATION DAMAGE NOW AND LATER

• Radiation damage to your body can occur in
  several ways
• Break apart essential molecules
• proteins (i.e. enzymes)
• nucleic acids (i.e. DNA)
• Mutations

• Kills cells
• Mutates sperm/ova
• Cancer
• Government recommends no greater than exposure to
  500 mrem per year for general public
• Government recommends no greater than 5,000 mrem
  per year from the workplace

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Table of Factors Effecting Biological Damage from
Radiation
Factor Effect
Dose Increase in dose produces proportional increase in risk
Exposure time Spreading out over time decreases risk
Area Exposed Larger area means greater risk
Tissue type Rapidly dividing cells more susceptible
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Radiation effects by dosage
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EXPOSURE TO RADIATION

• Exposure to radiation can come from
• Cosmic Rays
• Radioisotopes in rocks, soil, water, air
• Fallout from nuclear weapons testing
• Air travel
• Radioisotope release from nuclear power
  generation

• Government recommends no greater than exposure to
  ______________for general public
• Government recommends no greater than ___________
  per year from the workplace

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RADON IN HOMES

• Radon gas comes from Gas released from earth
  (from Uranium decay
• Radon gas exposure can lead to lung cancer
• ___________ of lung cancer deaths are caused by
  radon exposure.
• ___________ of households in the U.S. have
  higher than recommended radon levels.

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